Question

Among the following parameters HTST pasteurizer instrumentation, one that is not a controlling operation

• A. Pneumatic signal to steam valve
• B. Electrical signal to Temperature Comparator
• C. Pneumatic signal to thermograph pen
• D. Signal to alarm

Hint:

Instrumentation Functions:
Controlling Operations = Steam valve actuator, Flow diversion valve, Alarm triggers.
Indicating Recording Operations = THERMOGRAPH PEN (Passive chart recording).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Industrial process control loop architectures: active controlling operations manipulate final control elements (valves, alarms, solenoids), whereas signals driving a thermograph pen are passive recording/indicating operations.
Key Formula or Approach:
\[ \text{Control Loop: Sensor (RTD)} \rightarrow \text{Comparator (Control)} \rightarrow \begin{cases} \mathbf{\text{Steam Valve / Flow Diverter}} \& \text{Controlling Action} \mathbf{\text{Thermograph Pen}} \& \mathbf{\text{Recording / Indicating Action ONLY}} \end{cases} \]

Step 2: Detailed Explanation:
In dairy automation, instrumentation, and HTST pasteurizer control loops:
1. Controlling Operations (A, B, D): Direct actions that alter system status or maintain process setpoints:
- Signal to Steam Valve (A): Modulates hot water/steam flow to correct pasteurization temperature.
- Signal to Temperature Comparator (B): Compares measured temperature with setpoint ($72^\circ ext{C}$) to generate controller error signals.
- Signal to Alarm FDV (D): Triggers diversion valve and alarms during under-temperature conditions.
2. Pneumatic Signal to Thermograph Pen (C): A mechanical recording/logging mechanism that physically draws the temperature trace on the circular paper chart. It serves strictly as an indicating and record-keeping function, NOT a controlling operation.

Step 3: Final Answer:
Hence, Pneumatic signal to thermograph pen is not a controlling operation, matching option (C).